Over the past 10 years, if there had been a fund generating about £25m a year, we could have solved the problem of the vanishing works of art by buying them for the nation. Instead, we have spent in the best years about £9m, and in the worst only half a million, to meet this problem. In the current year we already have, as it happens, a much larger task: Reynolds's Omai and Raphael's Madonna of the Pinks will between them cost £40m, and it is generally agreed that the system has broken down.

Or rather, one part of the system has broken down: the system for raising the money. The other part of the system, whereby works of art are assessed for their significance, is in perfectly good shape. There is a committee of experts working for the Department of Culture, Media and Sport, known colloquially as the Waverley committee, named after Lord Waverley (who also invented PAYE and gave his family name to the Anderson shelter).

The Waverley committee re-views the objects that come be-fore it, asking whether they meet any one of three criteria - the Waverley criteria.

The first is: "Is the object so closely connected with our history and national life that its departure would be a misfortune?" Those who favour saving Reynolds's portrait of Omai over the Raphael Madonna (I am strongly in favour of saving both) tend to be arguing along the lines of this criterion.

But remember - the rules are that any one of the three criteria is enough. The second criterion is: "Is it of outstanding aesthetic importance?" And the third: "Is it of outstanding significance for the study of some particular branch of art, learning or history?" On either of the last two criteria, the Madonna of the Pinks , the product of the moment when Raphael first encounters the art of Leonardo da Vinci, passes, as it were, by acclamation.

Once it has made its recommendation for an export stop, the committee has done its work. And it is work that, by general agreement, the committee does well. When critics cry foul, it is generally decisions of past ministers they are pointing to, not the workings of the reviewing committee.

What about setting up an endowment fund and putting it at the disposal of this admirable body of experts? What about, that is, taking one whacking great sum of money (or a limited series of sums over the next few years), and investing it, and putting the income in the hands of the Waverley committee? That way, when the committee says no to an export, no means no.

The idea was first put to me by David Scrase of the Fitzwilliam Museum, Cambridge. I have tried it out on several interested parties in museums and galleries, and it seems to cheer up a lot of them. It builds on the merits of the present system, and addresses its main defect. But it is true it makes the Waverley committee suddenly very powerful.

The question arises: who would allocate the objects bought by the committee? Well, if the committee itself could make such allocations, it would become possible for a large number of muse ums to think of owning works of art they cannot dream of now, because they cannot find matching funds.

The York Art Gallery could argue that Omai should come to York, as it is from a great Yorkshire collection. The Raphael Madonna might be put in for by the Hatton Gallery in Newcastle, where incidentally it was exhibited among treasures from Alnwick some time before its identification as an original Raphael.

The committee could reject these applications and decide that works of such significance should go to national collections. At least they would be able to make have a choice in the matter. At the moment, the National Gallery is going for the Raphael in part because no other institution in the country can come remotely near to acquiring it. (The gallery itself is hoping to stump up about a third of the cost.)

When people say, "But the National Gallery already has enough Raphaels," they forget this point. Often when I ask people whether they would be keener to save the Raphael for the nation if it were being bought for, say, Liverpool or Bristol, they agree they would be. Well, before that can happen we need a new system, and before we get a new system we have to address the crisis in hand.

A lump sum of £500m, invested 10 years ago as an endowment fund, would have seen us through the problems that have arisen over the export of significant works of art. And (admittedly assuming the fund was well invested), the money would still be with us now. Our museums and galleries would be so much the richer. Those with funds for acquisitions could concentrate on collecting in new areas, instead of desperately responding to these export crises - these crises which will not go away, by the way, but will get worse, unless something imaginative is done.